At present, a sintered hard alloy containing more than 70 mass % of WC and a cermet containing Ti as the main component are used as cutting tools. The sintered hard alloy has high wear resistance and high fracture resistance and has been widely used for cutting tools. However, due to the price rise of WC raw materials, it has been examined to reduce the use amount of the WC by replacing the WC by other materials. On the other hand, the cermet has wear resistance higher than that of the sintered hard alloy but has a problem in that the fracture resistance is lower than that of the sintered hard alloy, which limits the use thereof.
For example, Japanese Unexamined Patent Application Publication No. 2009-275237 discloses a cermet containing three kinds of hard phases of WC, Ti(C, N), and (Ta, Nb)C at a predetermined ratio. Moreover, NPL 1 discloses adding 20 to 50 volume % of WC raw materials to a cermet, and then firing the same while adjusting a nitrogen current atmosphere and a vacuum atmosphere to thereby form a surface portion with a predetermined thickness (portion in which the presence ratio of carbide, nitride, and carbonitride of metals of Groups IV, V, and VI in periodic table, other than WC, is low and the presence ratio of WC is high) on the surface of a sintered compact.
The following is a list of aforementioned background art
PTL 1: Japanese Unexamined Patent Application Publication No. 2009-275237
Non Patent Literature
NPL 1: Daisuke TAKEZAWA and other 4 persons, “Influence of WC Addition Amount and Firing Atmosphere on Superficial Region Formation of WC Phase Remaining Cermet”, Japan Society of Powder and Powder Metallurgy Autumn Meeting Lecture Collection in 2010, p. 105
However, with the cermet (hard alloy) in which the three kinds of hard phases are dispersed as in Japanese Unexamined Patent Application Publication No. 2009-275237, the hardness of the alloy has become high to increase the wear resistance of tools but the fracture resistance of the alloy has not been sufficient. Even the hard alloy in which the surface portion is formed on the surface of the alloy as in Daisuke TAKEZAWA and other 4 persons, “Influence of WC Addition Amount and Firing Atmosphere on Superficial Region Formation of WC Phase Remaining Cermet”, Japan Society of Powder and Powder Metallurgy Autumn Meeting Lecture Collection in 2010, p. 105 has had a problem in that the fracture resistance of the alloy has been inferior to that of the sintered hard alloy.
The present invention is to provide a hard alloy and a cutting tool with reduced WC content and improved fracture resistance.